Years before prosecutors say he illegally financed an election effort for Mayor Vincent C. Gray, a local businessman allegedly secretly spent hundreds of thousands of dollars on behalf of at least seven other candidates for mayor and the D.C. Council, according to several people familiar with the payments.

Jeffrey E. Thompson, who is under federal investigation for allegedly financing a $653,000 secret campaign for Gray in 2010, allegedly made similar expenditures dating back to at least 2006, according to two people with direct knowledge of the payments who spoke on the condition of anonymity because the investigation is ongoing.

Thompson boosted the mayoral campaign of Linda W. Cropp, a Democrat, seven years ago with more than $100,000 in alleged illegal spending, the people said. He allegedly spent smaller amounts on behalf of former council member Michael A. Brown and the insurgent council candidacies of Patrick D. Mara, a Republican, and Mark H. Long, an independent, in 2008. And he allegedly spent still more in 2010 for council hopefuls Jeff Smith and Kelvin Robinson, both Democrats, and in 2011 for council member Vincent B. Orange (D-At Large).

Though the sums of money were significantly smaller than the amount that went into what has become known as the “shadow campaign” for Gray in 2010, such expenditures could reveal a pattern in which Thompson appears to have wielded vast influence for years over the District’s political process.

Cropp and Mara denied any knowledge of the payments, as Gray has done regarding the alleged secret effort to help him in 2010. The other candidates either couldn’t be reached or, through attorneys, declined to comment.

That keeps the focus of a21/2-year investigation into political corruption in the District, for now, on Thompson.

Prosecutors appear to be methodically building a case against Thompson, who was for years one of the District’s largest contractors and who, court records suggest, is the subject of a grand jury investigation.

An individual matching Thompson’s description has been mentioned on numerous occasions in court documents as allegedly funding the “shadow campaign” for Gray (D) as well as arranging illegal “straw” donations made with his own money but disclosed as coming from employees and other associates.

While declining to comment on any particular allegations of wrongdoing, Bill Miller, a spokesman for the U.S. attorney’s office, issued a statement Friday that said: “It is clear from our office’s public corruption prosecutions over the past several years that we will not excuse criminal activity as business as usual. We plan to continue vigorously investigating and prosecuting crimes that deprive D.C. voters of the fair and transparent elections that they deserve.”

Most recently, Thompson secretly paid for T-shirts, campaign signs and field workers in 2011 to help return Orange to office, the individuals asserted. In that campaign, Orange relied on some of the same players implicated in the parallel campaign for Gray the prior year.

One of those people, veteran field organizer Vernon E. Hawkins, recently has been in talks with federal prosecutors about entering a possible plea agreement in connection with his work on the Gray shadow campaign, according to several people familiar with the negotiations who, like others, spoke on the condition of anonymity because the investigation continues.

The deal, which will not be final until a judge accepts it, is expected to be made public as soon as this week, according to two people with knowledge of the investigation. If charges are filed, Hawkins would become the latest in a series of Thompson associates to be implicated in the scandal.

William E. Lawler III, Hawkins’s attorney, declined to comment on the allegations that his client was involved in unreported expenditures for other campaigns. He also declined to comment on whether Hawkins has signed a plea agreement with federal prosecutors or whether there are any plans to do so.

Thompson’s alleged activities were often, but not always, coordinated with his longtime associate Jeanne Clarke Harris, a public relations consultant who admitted in federal court last year to participating in the shadow campaign for Gray by funneling Thompson’s money through companies she owned.

Brendan V. Sullivan Jr., an attorney for Thompson, could not be reached and generally does not comment on his cases. Harris attorney Mark H. Tuohey III did not respond to an e-mailed request for comment.

City campaign finance laws impose limits on donations and spending and require political committees to report their activities even if they are not officially coordinated with a campaign.

In recent months, prosecutors have obtained guilty pleas from two other Thompson associates who admitted being a part of what U.S. Attorney Ronald C. Machen Jr. called an “assembly line” for donations run out of Thompson’s firm.

Brown, the former council member who had been a Democrat but ran as an independent in 2008 and 2012, also admitted to secretly accepting money from Thompson. He told prosecutors that Thompson provided him with a $20,000 payment, sending it through a company Harris owned. Brown then reported it as a donation of his own money to his 2008 campaign.

Little has been publicly aired, however, about alleged illegal spending in support of other candidates Thompson favored in the years before the 2010 mayor’s race and in the 2011 at-large council contest.

The money, according to the people familiar with Thompson’s spending, allegedly went to support a variety of activities, from campaign literature and canvasser stipends to election-day food and transportation for voters and poll workers.

None of the candidates received support to the extent that Gray did, the individuals with knowledge of the expenditures said, and the candidates Thompson backed did not always win. But the alleged undisclosed assistance appears to have allowed the city businessman to skirt campaign finance limits and not reveal to incumbents that he was backing their long-shot challengers.

Federal investigators are aware of the alleged unreported spending on behalf of some of the other candidates and have reviewed receipts and other records that document some of the payments, according to two people close to the investigation. The three-year statute of limitations to file misdemeanor campaign finance charges has expired in most cases.

Cropp, the former council chairman who lost to former mayor Adrian M. Fenty (D) in the 2006 mayoral primary, said she had no knowledge of any illicit spending made by Thompson for her campaign. “We had a campaign that was above board,” she said Wednesday.

She called Thompson a “good fundraiser” for her campaign but said she was unaware of any other activities he had undertaken.

“In that campaign, I was busy,” she said. “I had never been busier. All I wanted to do was my job as chairman, and I campaigned very hard.”

Campaign finance records show that Cropp’s 2006 campaign made a series of publicly reported payments to one of Harris’s firms, Details International, totaling more than $68,000 for a wide range of services listed as advertising, campaign materials and rentals.

Off the books, the sources asserted, Thompson spent more than $100,000, covering additional costs for campaign materials and transportation for canvassers and voters.

Mara, who won the 2008 Republican primary but lost to Brown in the general election, said he was not aware of any payments Thompson made on behalf of his primary campaign.

Former council hopefuls Robinson and Long, who went on to serve as Gray’s driver during the 2010 mayoral race, did not return messages seeking comment. Smith could not be reached. Brian M. Heberlig, an attorney who represented Brown in his June guilty plea to a federal bribery charge, declined to comment because of his client’s ongoing cooperation with the government’s investigation.

Thompson, according to two people with knowledge of the arrangement, backed Orange during his 2010 run for council chairman. But the more serious effort came in 2011, the individuals said, when Orange won a special election to fill the at-large seat vacated by Kwame R. Brown (D), who had defeated Orange in the chairman’s race.

Some of the same figures known to have had roles in the Gray shadow campaign helped Orange that year, according to several individuals with direct knowledge of both campaigns.

According to interviews with several Orange campaign workers, Hawkins was a regular attendee at high-level campaign meetings, helping to organize field outreach and participating in strategy discussions. Harris, too, was seen on several occasions at the campaign’s Georgia Avenue office, several workers said. At least three other Orange 2011 staffers had also worked on the Gray shadow effort, those workers said.

Andi Pringle, a political consultant who worked for the 2011 Orange campaign, confirmed that Hawkins advised the Orange campaign and said that she saw Harris at the campaign office before the election.

Hawkins, who was employed at the time as an administrator for Union Temple Baptist Church in Anacostia, does not appear on campaign finance reports Orange filed for the 2011 campaign. Workers said Hawkins was reticent to be formally associated with the campaign, asking not to be included on mass e-mails and, in at least one instance, telling workers in a meeting they were to refer to him only as “Eugene.”

At least two Orange workers have been interviewed by federal authorities in recent months. One reported being shown invoices and receipts for political activities that were not listed in the campaign’s public financial disclosures.

Orange and his campaign aides have not been named in court documents. Orange did not respond to several phone messages and e-mails seeking comment. Joseph F. Johnson Jr., the campaign’s chairman, declined to comment.

Orange previously disclosed that, during the 2011 campaign, he accepted $26,000 in contributions, largely through money orders, that were later connected to Thompson or Harris. During his reelection campaign last year, Orange said he considered those donations — some of which featured similar handwriting and sequential serial numbers — “suspicious and questionable” upon closer examination, but he later claimed vindication after a city audit.

Ann covers legal affairs in the District and Maryland for the Washington Post. Ann previously covered state government and politics in California, New Hampshire and Maryland. She joined the Post in 2005.

Mike DeBonis covers Congress and national politics for The Washington Post. He previously covered D.C. politics and government from 2007 to 2015.

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